1. Field of the Invention
The present invention relates to an imaging apparatus that has the function of compressing the dynamic range of images, and to a method of processing images.
2. Description of the Related Art
In most imaging apparatuses, the dynamic range of an image is compressed, thereby to reduce the difference in brightness between the parts of the image.
Two methods of compressing the dynamic range are available. One method is to correct the gradation of the entire image. The other method is to correct the gradation of only the low-frequency components of the image. In the former, the gradation is corrected by means of the gamma correction, the knee correction, or the so-called histogram equalization, thereby compressing the dynamic range. In the latter, the gamma correction, the knee correction or the like is performed, thereby compressing the dynamic range.
In most cases, an image whose dynamic range must be compressed is one obtained by applying two or more illumination light beams that greatly differ in intensity. A method is available, which can effectively compress the dynamic range of such an image (see Jpn. Pat. Appln. Laid-Open Publication 2001-275015). In this method, the parts of the image, other than the edges, are smoothed, while leaving the edges unprocessed. Next, a compression ratio is determined from the level of the parts smoothed. Finally, the dynamic range of the entire image is compressed in accordance with the compression ratio.
In this method, the image smoothed is a control signal. The minute amplitude-components remain uncompressed. The method therefore can provide images that can be well recognized visually, because their dynamic range has been compressed.